The present invention relates to the general technical field of agricultural machinery. The invention concerns a single-seed sowing machine having a chassis that supports at least one sowing element provided with a distribution box, at least one opening disk making it possible to open a furrow in the soil and a depth-control wheel, wherein the said distribution box delivers the seeds one-by-one via a rotary dosing element designed to turn around an axis of rotation and each seed is ejected from the rotary dosing element at an ejection point extending into the lower part of the rotary dosing element.
In some known sowing machines of this type, the distribution box is positioned at the rear of a plow, which has the function of placing seeds in the furrow. This plow extends between and to the rear of a double disk for opening the furrow, and it keeps the furrow open until the seed is deposited therein. Control of the sowing depth is achieved by means of a depth-control wheel. The depth-control wheel is offset to the front or rear of the plow. Such a sowing element is supported on the soil via two contact points. The first contact on the soil is established by the depth-control wheel and the second via the plow. Each obstacle and/or irregularity of the soil therefore always results in two perturbations for the sowing element, since the support on the soil is established at the depth-control wheel and at the plow. The sowing precision is altered by these perturbations. Furthermore, the precision of sowing is also impaired by the fact of wear of the plow.
On other sowing machines, the distribution box is mounted above the double opening disk and a transfer means makes it possible to guide the seeds into the furrow as it is being formed. During sowing, only the depth-control wheels are in contact with the soil. With a single point of contact with the soil, the sowing quality achieved by each sowing element is optimum. On the other hand, such a configuration has a seed discharge approximately 50 cm above the soil, and so the seeds are guided by the transfer means. This large discharge height impairs the sowing precision. In general, the type and weight of the seeds modify the speed at which the seeds fall, because of the fact of the influence of gravity.